Furnace control system



March 3, 1942. H. G. MEAD FURNACE CONTROL SYSTEM Filed Jan. 11, 1940 2Sheets-Sheet l March 3, 1942. H. G. MEAD I FURNACE CONTROL SYSTEM FiledJan. 11., 1940 2 Sheets-Sheet 2 Patented Mar. 3, 1942 UITE STATES rricFURNACE CONTROL SYSTEM Application January 11, 1940, Serial No. 313,367

8 Claims.

My invention relates to control of rate of input of heat to a continuousfurnace to ensure that the temperature of the billets, slabs, or thelike, at discharge from the furnace is of desired or predeterminedmagnitude different from that of the furnace.

In accordance with my invention, the temperature of the billets ismeasured as they in succession approach the discharge end of the furnaceby a radiation pyrometer having a sighting tube extending through wallstructure of the furnace with its open end adjacent the path of thebillets and provided with, or constructed to serve as, a shield limitingthe radiation measured substantially entirely to that from the billetsthemselves to the exclusion of radiation from sources at the same orother temperatures, such as wall structure and the like within thefurnace; preferably a fluid medium, such as air or other suitable gas,is forced through the tube to protect the pyrometer from overheatingand, which is more important, to keep the path of radiation to thepyrometer from the billet surface under observation free of smoke,fumes, flames or other medium.

Further, in accordance with my invention, the heat input to the furnace,or to one or more zones thereof, is automatically controlled by theradiation pyrometer to control, preferably maintain equal and uniform,the temperatures of the successively discharged billets.

My invention further resides in the features of construction,combination and arrangement hereinafter described and claimed.

For an understanding of my invention, reference is made to theaccompanying drawings in which:

Fig. 1 is an elevational view, with parts in section, of the dischargeend of a furnace and associated control apparatus;

Figs. 2, 2A, 3 and 3A, in perspective and on enlarged scale, illustratemodifications of shield structure shown in Fig. 1;

Fig. 2B is a detail view, on enlarged scale, of one of the link elementsof Fig. 2A;

Figs. 4, 5, 6A, 6B and 6C are explanatory figures referred to indiscussion of the control system of Fig. 1;

Fig. 'lis an elevational view, in section, of a furnace having severalheating zones.

Referring to Fig. 1, there is shown the dis charge end of furnace Fexemplary of the type used for heating billets, slabs, or the like totemperature suitable for rolling, drawing, or equivalent operation. Inthe particular furnace shown, the billets B are pushed along theinclined floor i of the furnace in the direction of the arrow and eachin turn slides down the steeper incline 2 for discharge from the furnacethrough and beyond its door 3; any other suitable arrangement forfeeding the billets through the furnace may, of course, be utilized.

The heat input to the furnace is supplied by a plurality of burners 4directed into the heating chamber or zone 5, generally through the sideand end walls, and is controlled by valves 6 in the fuel lines 1supplying gas, oil or other fuel to the burners.

In the operation of furnaces of this type, the billets do not, exceptoccasionally by chance, remain in the furnace long enough to effectequality of their temperature with the furnace temperature; it hasheretofore been the practice in the operation of such furnaces tocontrol the heat input to maintain the furnace temperature constant atpredetermined magnitude suitably higher than the desired rollingtemperature of the billets; otherwise stated, it was sought to maintaina constant temperature head or constant temperature differential. Tothat end, the furnace temperature was measured by thermocouples withinprotecting tubes inserted through the furnace walls. However, because ofsuch factors as variations in the rate of billet feed through thefurnace, in the number of billets within the furnace at different timesin a run, in the room or ambient temperature, in the absorption of heatby the furnace walls and in the effect of flame and smoke upon theresponse of the thermocouple, the temperature of the discharged billetswas not uniform throughout a run but varied to substantial extent withconsequent adverse effect upon the rolling operations. With this priormethod of control, it was not unusual for the temperatures of differentbillets to vary as much as 300 F.

With the control system of Fig. 1, the heat input to the furnace is notcontrolled in accord with the temperature of the furnace, but in accordwith the temperature of billets within the final zone of the furnace;thetheat input to the furnace is varied in proper sense and extent toobtain the uniformity of the billet temperature regardless of whetherthe consequent changes in heat input increase or decrease the furnacetemperature.

As the billets move through the final zone of furnace F, they in turnpass, during continuous, open and unrestricted exposure to the furnaceatmosphere or gases, adjacent the open or apertured end of the tube 8extending through a wall, specifically the roof 9, of the heatingchamber 5. At or upon the other end of tube 8 is mounted a radiationpyrometer unit or head l0, preferably of the multi-couple type disclosedin Letters Patent 2,232,594, granted February 18, 1941, to Dike upon hisapplication Serial No.

' 215,499, filed June 23, 1938, for producing an electromotive forcerepresentative of the quantity of radiation entering the lower open endof tube 8. To exclude from the measurements the eifect of radiation fromthe furnace walls or from the flames, the lower end of tube 8 isprovided with a shield ll, attached to or integral therewith, andextending outwardly to suitable extent from the periphery of tube 8. Thetube and shield are of non-metallic refractory material, such asCarborundum, or of metal or metal alloy such as nickel-chromium alloysuited to afford reasonably long life at the temperatures involved whichmay be, for rolling steel billets, generally of the order of 1500 F. to2200 F. The tube 8 may conveniently be of circular crosssection and, forexample, of about 3 or 4 inches in diameter; its length is determined bythe size of the furnace and the location of the pyrometer head.

In those installations in which there is danger of the billets piling upor for some other reason striking the lower end of tube 8 or shield ll,

there may be utilized the modified arrangement shown in Fig. 2 in whichthe tube 8 terminates well above the path of the billets, the plate Hand the closely spaced chains A depending therefrom serving as a shieldto prevent radiation from the walls of the furnace and from the flamefrom being reflected by the upper face of the billets into the sightingtube. The chains 1 IA yield in event they are struck by a billet pi edup upon another or otherwise out of position, but upon passage of thebillet the chains return to their normal positions and so preserve theintegrity of the shield.

In the similar arrangement shown in Fig. 2A, the flexible shieldstructure A comprises plate links I 9, Fig. 2B, suitably joined to forma curtain for interception of radiation to the upper face of a billetunder observation from the fumace' walls or the flame.

Other suitable and preferred forms of shield are shown in Figs. 3 and3A; in both figures, the shield is a funnel or cone-shaped membersuitably fastened at its smaller end to the lower end of tube 8; in Fig.3 shield B is attached by bolts to a flange 8A extending outwardly fromthe lower end of tube 8; in Fig. 3A, the lower end of tube 8 is providedwith bayonet slots 16 for receiving pins I! extending radially fromsleeve l8 at the upper end of conical shield NC.

The path of radiation from the billet surface under observation to thepyrometer head I is maintained free of smoke and flame, or other mediawhich would otherwise cause the output voltage of the radiationpyrometer unpredictably to vary to magnitudes lower or higher than thevoltage corresponding with the billet temperature, by forcing air,orother suitable fluid medium, downwardly through tube 8. In theparticular arrangement shown,-a small blower I! having its dischargeduct l3 connected to tube 8 outside of the furnace and adjacent thepyrometer head continuously forces air through tube 8. The stream of airin addition to maintaining the sighting tube 8, substantially free ofsmoke and flame, also serves to cool it and so prolongs its effectivelife.

The absorption of radiation by the introduced air is a constantcompensated for by the calibration of the pyrometer.

The thermocouple device within pyrometer l0 may connect to any suitablevoltage-responsive device or arrangement, for example, a voltmeterprovided with a scale calibrated in units of temperature, or a measuringnetwork such as a potentiometer having a rebalancing slidewireassociated with a temperature scale. With such information available tohim, an operator may manually adjust the fuel valves 6, or equivalentmeans for varying the heat input, to maintain the observed temperatureof the billets about to be discharged from the furnace at the desiredmagnitude. Preferably, however, control of the valves 6 or equivalent iseffected automatically as by controller I! which, for example, may be ofany of the types disclosed and claimed in U. S. Letters Patent 2,155,346to Davis, 2,154,065 to Davis et al. and 2,113,069 and 2,096,064 to Rosset al. With each valve 6 may be associated a reversible motor I3connected by conductors M to a control switch within controller l2which, in response to departure of the temperature of the observedbillets from their desired temperature, varies the heat input to thefurnace and particularly to the final zone thereof, in proper sense torestore the billet temperature to the desired magnitude; the instrument12 preferably is also, as shown in aforesaid patents, a recorder onwhose chart or record sheet l5 there is traced the temperature of thebillets.

The total-radiation pyrometer l 0 or equivalent automatic observer maybe replaced by an optical, or partial-radiation, pyrometer and a humanoperator who sights through tube 8 upon the billets B as they passbeneath the open end of tube 8 to determine their temperature. In suchmodification, the blower I2 is retained to maintain tube 8 free ofsmoke, flame or other media which would, by absorption or enhancement ofradiation, introduce errors into the observations; shield ll, HA, 3 or Cis also retained to preclude introduction into tube 8 of radiation fromsources, such as the furnace walls or flame, other than the billet orbillets under observation.

My method of control of the heat input compensates for or takes intoaccount all of aforesaid variable factors, including rate of feed of thebillets, the number of billets in the furnace, ambient temperature,absorption and radiation of heat from and by the furnace walls and so,notwithstanding variations in any or all of said factors, insuresuniformity of final temperature of the billets as discharged forrolling, forging or other similar operation. By way of example,

'a furnace controlled in accordance with my method discharged billetswhose temperature varied throughout a run only about 5 F. from thedesired temperature, whereas, with the same furnace controlled inaccordance with aforesaid previous practice, the billet temperatureoften varied, throughout a run, as much as 300 F.; i. e., from about1500 F. to about 1800 F.

This difference between the two methods'of control of heat input to acontinuous furnace is evident from comparison of Figs. 4 and 5;referring to Fig. 4, the curve FT illustrates the substantial constancyof the furnace temperature when the heat input thereto is controlled bya thermocouple disposed within a protecting tube which projects into theheating chamber and curve WT illustrates the undesirable resulting widevariations in final or discharge temperature of the billets. In contrasttherewith, the curve WT of Fig. illustrates the uniformity of the finalbillet temperature when the heat input is controlled by the arrangementshown in Fig. 1; the curve FT of Fig. 5 illustrates the changes infurnace temperature, or the changes in 'temperature head required toobtain aforesaid uniformity of the billet temperature.

The sensitivity of the pyrometer of Fig. 1 to changes in temperature isso high that there is indicated or recorded the variations intemperature along the individual billets; consequently, when the recordof the billet temperature appears, as in Fig. 6A, with a series of teethinclined to the right, toward higher temperature,

it indicates the preliminary zone 5A of the furnace F (Fig. 7) is coolerthan the final zone 5, whereas, when the preliminary zone 5A is hotterthan the final zone, the record appears as in Fig. 6B with the saw teethinclined to the left indicating that each billet has decreased intemperature as it moved in the final zone below tube 8. When the burner4A of the preliminary zone 5A are adjusted for proper or optimum heatinput to that zone, the'record of the final billet temperature, asappears in Fig. 6C, is a smooth curve devoid of abrupt breaks or sawteeth.

The burners in the preliminary zone or subdivisions thereof may becontrolled manually or automatically in response to the sense of changein temperature of the billets as they pass along the final zone.

The temperature of the billets at any one or more stages of or points intheir progress through the furnace may be measured by any of theradiation-pyrometer arrangements herein described, and, if desired, theheat input to any one or more zones of the furnace may be controlled inaccordance with such measurement, as broad- 1y exemplified by control ofheat input in response to temperature at the discharge end or finalzone, Fig. 1.

The unit, comprising sighting tube 8 with a radiation pyrometer or otherradiation-responsive device at one end thereof, and with a radiationshield extending outwardly therefrom at or adjacent the other end, isnot limited to use in a continuous furnace; it is utilizable toadvantage as well in other types of furnaces, such for example ashardening or annealing furnaces, in which it is desired to measure thetemperature of the Work with avoidance of errors due to reflection fromthe work surface of radiation from other sources, such as the wallstructure of the furnace or flame, or due to absorption of radiationfrom the work surface by smoke or fumes in the furnace.

For brevity in the appended claims, it shall be understood the termbillet" is generic,-and comprehends billets, slabs, or other masses orpieces of steel or other metal, or non-metallic objects, generally oflike forms or dimensions.

The term sighting" as herein employed is not limited to observation bythe human eye, but is used, as common in pyrometry, also to comprehendobservation or sighting by any radiationresponsive element, such as aradiation pyrometer photo-electric cell or equivalent device,

" preferably one which produces an electrical efifect of magnituderepresentative of the temperature of the billet under observation.

What I claim is: 1. A system for measuring the temperature of billetswithin a continuous furnace comprising 76 a radiation pyrometer providedwith a sighting tube extending lthrough wall structue of the furnace andhaving an open end disposed adjacent the path of said billets to view asurface of each of the successive billets during continuous andunrestricted exposure of said surface to the furnace atmosphere, andstructure adjacent said open end of the sighting tube and extendinglaterally therefrom to prevent radiation from the interior of thefurnace from being reflected into said tube by the surface of a billetunder observation by the pyrometer and without interruption of exposureof that surface to the furnace atmosphere.

2. An arrangement for measuring the temperature of work within a furnacecomprising a radiation pyrometer provided with an openended sightingtube having its open end adiacent the work to view a surface thereofduring continuous, open and unrestricted exposure of said surface to thefurnace atmosphere, and means for preventing effect upon themeasurements by fiame, smoke or reflections within the furnacecomprising means for forcing a fiuid medium through said tube, and aradiation shield extending laterally from said open end of the tube andat suitable distance from said surface of the work for unrestrictedaccess to said surface of said furnace atmosphere.

3. An arrangement for measuring the temperature of work within a furnacecomprising a radiation pyrometer provided with an openended sightingtube having its open end adjacent a surface of the work duringcontinuous, open and unrestricted exposure of said surface to thefurnace atmosphere and having said end flared to prevent radiation fromother sources thereof within the furnace from directly reaching thepyrometer or indirectly by reflection from said exposed surface of thework.

4. An arrangement for measuring the temperature of work within a furnacecomprising a radiation pyrometer provided with an openended sightingtube having its open end adjacent the work to view a surface thereofexposed to the furnace atmosphere, and structure adjacent said open endof said tube and extending laterally therefrom to prevent transmissionthrough said tube to the pyrometer of radiation from a source other thansaid surface of the work itself without restriction of exposure of saidsurface to the furnace atmosphere.

5. A system for measuring the temperature of billets within a continuousfurnace comprising a radiation pyrometer provided with a sighting tubeextending through wall structure of the furnace and having an open endadjacent the path of said billets to view a surface of each of thesuccessive billets during continuous and unrestricted exposure of saidsurface to the furnace atmosphere, and a plate supported adjacent saidopen end of said tube and extending laterally therefrom to preventradiation from flame and from wall structure of the furnace fromstriking the billet surface under observation by the pyrometer withoutinterruption of aforesaid continuous and unrestricted exposure of thatobserved surface to the furnace atmosphere.

6. A system for measuring the temperature of billets within a continuousfurnace comprising a radiation pyrometer provided with a sighting tubeextending through wall structure of the furnace and having an open endadjacent the path of said billets, and a plurality of yielding membersclosely spaced about said open end of said tube to define a shieldpreventing impingement upon that portion of the billet surface underobservation by the pyrometer of measurement affecting radiation from asource other than said surface portion itself.

7. A system for procuring equality of the temperatures of billetsdischarged from a continuous furnace comprising a radiation pyrometer,for

measuring the temperature of successive billets as they approach thedischarge end of the furnace, a sighting tube for said pyrometerextending through wall structure of the furnace and having an open endadjacent the path of the billets to view a surface of each of thesuccessive billets during continuous and unrestricted exposure of saidsurface to the furnace atmosphere, structure disposed adjacent andextending outwardly from said open end of the sighting tube to preventreflection of radiation from the interior of the furnace into said tubeby the exposed surface of the billet under observation by the pyrometerwithout interruption of exposure of that surface to the furnaceatmosphere, and

means for varying the heat input to the furnace in accordance with themeasured temperature of the billets.

8. A system for procuring equality of the temperatures of billetsdischarged from a continuous furnace comprising a radiation pyrometer,for measuring the temperature of successive billets as they approach thedischarge end of the furnace, and a "sighting tube extending throughwall structure of the furnace and having an open end adjacent the pathof the billets to view a surface of each of the successive billetsduring continuous and unrestricted exposure of said surface to thefurnace atmosphere, means for preventing effect upon the measurements byflame, smoke and reflections within the furnace comprising means forforcing gas through said tube and shield structure projecting laterallyof its said open end to prevent reflection into the tube from the billetsurface under observation of radiation from flame and wall structure ofthe furnace and spaced at suitable distance from said surface to permitunrestricted flow of said gas and continuous, open and unrestrictedexposure of said surface to the furnace atmosphere. and means forvarying the heat input to the furnace in accordance with the measuredtemperature of the billets.

HAROLD G. ME

